The present invention relates to cooling, demonomerizing and dedusting gas from a thermoplastic polymer drier.
At the end of the process for manufacturing certain thermoplastic polymers (like polyamides (nylons), polyesters, polyolefins, polyacrylates, polysulfones, polyethersulfones, polyacetals, polyvinyl-chloride, and polyurethanes) pellets, granules or chips are formed which are often cooled with water. These wet pellets, granules or chips are usually dried in a drier with a gas at an elevated temperature.
It is advantageous to recycle the gas to the drier. However, the gas exiting the drier contains polymer dust, monomers, oligomers and water which have to be separated from the gas in order to recirculate the gas in the drying process. This separation may be performed in several separate steps like a dedusting step (for example in a cyclone or a filter or a combination of both) and a separate cooling step.
The separation efficiency of the cyclone or the filter is not always satisfactory. Dust not separated in the cyclone or filter is deposited in the gas cooler and eventually causes pressure loss in the gas circulation. Monomers not removed deposit on the connecting pipes, e.g., the pipes connecting the polymer drier to the cyclone. Therefore, there remains a need in the manufacture of thermoplastic polymers and other processes where efficient separation of dust and byproducts, such as monomers and oligomers, from gas exposed to such things. There also remains a need to clean such gas in one step.
Accordingly, the present invention improves efficiency for a process for cooling, demonomerizing and dedusting gas from a thermoplastic polymer drier by directing the gas, containing thermoplastic polymer dust, monomers, oligomers, and water, into a packed column and washing the gas with a solvent.
It is an object of the present invention is to provide a process for cooling, demonomerizing and dedusting gas from a polymer drier all in one step and with high efficiency.
Related objects and advantages of the present invention will be apparent to those of ordinary skill in the art after reading the following detailed description.